Why do parents all of a sudden want to be strict?

my mother has always let us get by with anything now all of a sudden she makes up in her mind that i go snooping through her stuff when she's not home and trying on her close that i may be able to fit..( i wear xs and she wears a 2x sometimes 3x)...now since she wants to accuse me of doing things im not i dont even want to talk to her,ever!